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in rapid motion so that the contents are kept thoroughly agitated
The thorough mixing of the materials is essential to the success

of the process.    The zinc dust is added  in quantities of 3__4

grains at a time through the wide glass tube, which is closed by
a cork after each addition. The mixture soon becomes warm
and eventually boils. To prevent the liquid boiling over the
frothing is allowed to subside before fresh zinc dust is added.
The operation is usually completed in J hour, when the liquid,
which has first a deep
red colour (a/.obcnzene),
becomes pale yellow. To
examine the colour a
sample should be with-
drawn with a pipette
and filtered. The stir-
ring is continued for
another ..]. hour. A litre
of cold water is added
which precipitates the
hyclrazobcnzene. The
mixture of hydrazoben-
zene and zinc residues
is filtered at the pump
and washed free from
alkali with water. The

precipitate is then pressed clown and extracted with 750 c.c.
of spirit on the water-bath with reflux condenser and filtered.
On cooling in a freezing mixture, the hydni/.obcnzcne crystal-
lises in colourless plates, which are filtered and washed with a
little spirit. The mother liquor is used for a second extraction
of the zinc residues, and from the filtrate a further quantity
of hyclra/obenzene is precipitated with water. If the second
crop of crystals have a yellow colour crystallisation from alcohol
will remove it. Yield 30 35 grams.

•\ 3/,n  I GNuOIl ™ C,jII,,NII.NnCr,IJn -I- 3/11(011),,

.s\ —Colourless plates ; in. p. 125".
Kt'ih'titins.— i.   Heat   a  small  quantity  in  a  dry test-tube.
Notice the colour.   On cooling add a little writer and pour a few
drops into a bolutiou of sodium hypochloritc.    A violet

L  2